The present invention relates to a device for automatically adjusting a braking clearance for a disc brake of the type in which at least one friction pad is directly placed in frictional engagement with a disc rotor by means of a hydraulically-operated piston.
With disc brakes of the type above described, the deformation of a friction pad resulting from compression thereof or the deformation of a reaction portion of a caliper used with friction pads that straddle the disc rotor can produce an undesirable change in braking clearance. As a result of such an occurrence, a friction pad can remain engaged with the disc rotor even after brake release, thus giving rise to dragging. Attempts to eliminate these problems have resulted in various types of adjustment devices. For example, with one-shot adjusting mechanisms that provide a desired braking clearance with a single adjustment, the caliper and friction pads are provided with a rigidity high enough so as to undergo minimum deformation. However, such a system has the disadvantage of excessive weight resulting from the increased rigidity and strength of the caliper. Another proposal is a micro-adjusting mechanism in which the maximum adjustment of braking clearance obtained by a single braking operation is much smaller than the amount of friction pad wear that occurs in response thereto. In this mechanism, however, if a large braking clearance exists when the adjusting device is initially installed, it is necessary to repeat the braking operation many times in order to obtain the desired braking clearance. Also, the mechanism is more complicated.
The object of the present invention is to overcome the limitations noted above by providing a brake adjusting device that eliminates requirements for excessive adjusting action without an excessive increase in weight.